Method and apparatus for selecting enhanced dedicated channel transport format combination in CELL—FACH state and idle mode

Abstract

A method and apparatus for selecting an enhanced dedicated channel (E-DCH) transport format combination (E-TFC) in Cell_FACH state and idle mode are disclosed. A wireless transmit/receive unit (WTRU) transmits a random access channel (RACH) preamble and receives an index to an E-DCH resource in response to the RACH preamble. The WTRU may estimate a power headroom based on the maximum WTRU transmit power, power offset value, and the last successfully transmitted RACH preamble transmit power. The WTRU restricts an E-TFC based on the estimated power headroom, and selects an E-TFC based on a set of supported E-TFCs. The WTRU then generates, and transmits, a protocol data unit (PDU) based on the selected E-TFC.

1. A method for estimating a power headroom in Cell_FACH state and idle mode, the method comprising:
 a wireless transmit/receive unit (WTRU) receiving a power offset value; 
 the WTRU transmitting a random access channel (RACH) preamble; and 
 the WTRU estimating a power headroom based on a WTRU maximum transmit power, the power offset value and a last transmitted RACH preamble transmit power. 
 
     
     
       2. The method of  claim 1  wherein the power headroom is estimated by subtracting the power offset and the last transmitted RACH preamble transmit power from the WTRU maximum transmit power. 
     
     
       3. The method of  claim 1  wherein the WTRU estimates the power headroom every time a RACH preamble is transmitted during power ramp-up. 
     
     
       4. The method of  claim 1  further comprising:
 the WTRU sending scheduling information including the estimated power headroom to a network. 
 
     
     
       5. The method of  claim 1  further comprising:
 the WTRU receiving an index to an enhanced dedicated channel (E-DCH) resource in response to the RACH preamble; 
 the WTRU performing E-DCH transport format combination (E-TFC) restriction to determine a set of supported E-TFCs based on the estimated power headroom; 
 the WTRU selecting an E-TFC from the set of supported E-TFCs; 
 the WTRU generating a protocol data unit (PDU) based on the selected E-TFC; and 
 the WTRU transmitting the PDU. 
 
     
     
       6. The method of  claim 5  wherein the WTRU estimates the power headroom for a predetermined duration, following reception of the index. 
     
     
       7. The method of  claim 5  wherein the WTRU estimates the power headroom and performs E-TFC restriction every time a RACH preamble is transmitted during power ramp-up. 
     
     
       8. The method of  claim 5  wherein the WTRU estimates the power headroom, performs E-TFC restriction, and selects an E-TFC every time a RACH preamble is transmitted during power ramp-up. 
     
     
       9. The method of  claim 5  wherein the WTRU estimates the power headroom, performs E-TFC restriction, selects an E-TFC, and generates a PDU every time a RACH preamble is transmitted during power ramp-up. 
     
     
       10. The method of  claim 5  wherein the WTRU performs the E-TFC restriction based on the estimated power headroom for a first E-DCH transmission following a RACH preamble transmission. 
     
     
       11. A wireless transmit/receive unit (WTRU) comprising:
 a transmit/receive unit configured to transmit a random access channel (RACH) preamble, receive an index to an enhanced dedicated channel (E-DCH) resource in response to the RACH preamble, and transmit an E-DCH transmission using a selected E-TFC in a Cell_FACH state or idle mode; and 
 a controller configured to estimate a power headroom in a Cell_FACH state or idle mode based on a WTRU maximum transmit power, a power offset value, and a last transmitted RACH preamble transmit power. 
 
     
     
       12. The WTRU of  claim 11  wherein the controller is configured to estimate the power headroom by subtracting the power offset and the last transmitted RACH preamble transmit power from the WTRU maximum transmit power. 
     
     
       13. The WTRU of  claim 11  wherein the controller is configured to estimate the power headroom every time a RACH preamble is transmitted during power ramp-up. 
     
     
       14. The WTRU of  claim 11  wherein the controller is configured to send scheduling information including the estimated power headroom to a network. 
     
     
       15. The WTRU of  claim 11  wherein the controller is configured to perform E-TFC restriction to determine a set of supported E-TFCs based on the estimated power headroom, select an E-TFC from the set of supported E-TFCs, and generate a protocol data unit (PDU) based on the selected E-TFC. 
     
     
       16. The WTRU of  claim 15  wherein the controller is configured to estimate the power headroom for a predetermined duration, following reception of the index. 
     
     
       17. The WTRU of  claim 15  wherein the controller is configured to estimate the power headroom and perform E-TFC restriction every time a RACH preamble is transmitted during power ramp-up. 
     
     
       18. The WTRU of  claim 15  wherein the controller is configured to estimate the power headroom, perform E-TFC restriction and select an E-TFC every time a RACH preamble is transmitted during power ramp-up. 
     
     
       19. The WTRU of  claim 15  wherein the controller is configured to estimate the power headroom, perform E-TFC restriction, select and E-TFC, and generate a PDU every time a RACH preamble is transmitted during power ramp-up. 
     
     
       20. The WTRU of  claim 15  wherein the controller is configured to perform the E-TFC restriction based on the estimated power headroom for a first E-DCH transmission following a RACH preamble transmission.